1. Field of the Invention
The present invention relates to an ultrasonic vibrator and an ultrasonic motor using the ultrasonic vibrator.
2. Description of the Related Art
Conventionally, different types of ultrasonic motors have been known. For example, Japanese Patent No. 3311446 discloses an example of the ultrasonic motors.
Hereinafter, the ultrasonic motor disclosed in Japanese Patent No. 3311446 will be described as a typical one.
Ordinarily, ultrasonic motors are provided with ultrasonic vibrators. The ultrasonic vibrator is formed as described below.
First, for the ultrasonic vibrator, a plurality of first piezoelectric sheets which are thin and have a rectangular shape and a plurality of second piezoelectric sheets which are thin and have a rectangular shape are laminated to each other. A pair of internal electrodes are printed on each first piezoelectric sheet. A pair of internal electrodes are printed on each second piezoelectric sheet. The ultrasonic vibrator has a structure in which these first and second piezoelectric sheets are alternately laminated.
The internal electrodes are formed so as to extend to the side faces and the upper surface of the ultrasonic vibrator. Regarding these piezoelectric sheets, the internal electrodes are printed on green sheets made of lead titanate zirconate (hereinafter, abbreviated to PZT). Then, the green sheets are positioned, laminated, and fired. Thus, these piezoelectric sheets are formed into a piezoelectric laminate unit.
External electrodes are provided in the positions of the piezoelectric laminate unit where the internal electrodes of the ultrasonic vibrator are exposed (two sites as positive poles on the upper surface of the ultrasonic vibrator and two sites as negative poles on the side faces of the ultrasonic vibrator).
Further, in the piezoelectric laminate unit, the external electrode provided on the upper surface on the left side and the external electrode provided on the left side-face are connected to each other via a lead wire. Thus, an electrical terminal is formed. An alternating voltage, which is described below, is applied to this electrical terminal for phase A.
Moreover, in the piezoelectric laminate unit, the external electrode provided on the upper surface on the right side and the external electrode provided on the right side-face are connected to each other via a lead wire. Thus, an electrical terminal is formed. An alternating voltage, which is described below, is applied to this electrical terminal for phase B.
The polarization can be performed by application of predetermined DC voltages to the respective electrical terminals for the phases A and B.
Furthermore, in the piezoelectric laminate unit, a driving piece (friction projection) is bonded to the position at which the amplitude of the bending-vibration of the lower surface of the ultrasonic vibrator has substantially a maximum.
In the ultrasonic vibrator having the above-described structure, alternating voltages with a phase difference of π/2 are applied to the electrical terminals for the phases A and B, respectively. This excites the primary longitudinal vibration and the secondary bending vibration. Thus, a large elliptical vibration in a clockwise or counterclockwise direction is generated.
The ultrasonic motor using the ultrasonic vibrator further contains the following elements.
A through-hole is provided in the center of the ultrasonic vibrator. A pin for taking out a driving force is inserted and bonded in the trough-hole. Further, a pressing means which is engaged with the pin to press the driving piece in a predetermined direction, and a driven piece which is in contact with the driving piece of ultrasonic vibrator and is moved relatively to the driving piece. Thus, the ultrasonic motor is formed.
The driven piece is held on a linear guide. Thus, the driven piece can be slidingly moved while it is in contact with the driving piece and is guided by the linear guide.
In the ultrasonic motor formed as described above, alternating voltages with a phase difference of π/2 are applied to the electrical terminals in the phases A and B. Thereby, the primary longitudinal vibration and the secondary bending vibration are excited. As a result, a large elliptical movement is caused in the clockwise or counterclockwise direction. Thus, the driven piece is moved in the right and left direction.